People use eyes for viewing of surrounding world and the human beings are able thanks to eyes to navigate within space based on information about scene depth. Dimensional (stereometric) perception of a static image, which is produced in human brain when viewing two planar displaced images of the same scene, was already described in 1830s by Sir Charles Wheatstone. We are not able to clearly distinguish depth information when viewing two-dimensional image. In the case of vision with one eye, one is able to perceive depth on the basis of monocular phenomena only. Two eyes are required to view three-dimensional (stereoscopic) images. Binocular vision is perceiving of scenes or images with both eyes. Resulting images are reflected on retina and brain reconstructs the same to perception of dimensional appearance. Stereoscopy is a branch involved in displaying of dimensional images or frames whereas two frames created for left and right eye are called a stereo pair. Stereoscopic video frequency is viewing of a sequence of consecutive frames. Recently, stereoscopy has been widely applied in different scientific branches, in the field of entertainment industry or elsewhere. It is known that visualization technologies have been long used for three-dimensional (stereoscopic) imaging. These systems do not project just one image for both eyes but try to project one of a pair of separated views for each eye. Stereoscopic imaging of two images displayed next to each other is known. Historically, it is the oldest method used still today. Using stereo-viewers (so-called stereoscopes), two static images captured by cameras horizontally shifted by eye span (about 7 cm) and placed next to each other are viewed with glasses. Similarly to audio technology, this distance is usually called as stereo basis. Special cameras with two lenses were and are produced for these purposes. Thanks to digital imaging, the required shifted images can be created using special software applications from a digital image. Glasses allow either direct (where right eye views right component image and left eye views left component image) or cross viewing of the shifted images (where right eye views left component image and left eye views right component image). Experiments showed that the “crossed” viewing is what allows expansion of the field of vision and improvement of stereoscopic effect depth. Glasses with special prismatic optics have been developed for this imaging. In this case, the component images are crossed as well. The principle works also for movable images and therefore, it is theoretically applicable for television, however, special horizontal scanning is required. The advantages of these systems include sufficient brightness of resulting image because the contributions of brightness of the component images are fully added. The component images are often picture slides. Another of these 3D imaging principles is stereoscopic imaging of superposition of two shifted images (Anaglyph system). The viewed image consists of superposition of two component images (so-called anaglyph) concurrently taken by two cameras that are again horizontally shifted by distance of eyes and therefore, project a scene under different angles. In cinematography or project television screen, the component images are projected on canvas via colour filters (cyan and red). A viewer watches the screen with glasses with corresponding colour glasses. This colour filtration makes sure that each eye perceives just a component image and the brain produces spatial perception. This method of separation may in case of colour images distort colour perception of resulting virtual image. Many versions of this system have been gradually developed. One of them is for example Color Code 3D system where different colour combination is used (yellow-dark blue in filters of projectors and amber-dark blue in filters of glasses). Anachrome Method should be mentioned as well with substantially narrower stereo basis aiming at possibility to view anaglyph even without glasses—without dimensional perception, of course. A disadvantage of this method is—except for necessity of using special glasses—small permissible deviation from viewer's position from the image axis at which the spatial perception (stereoscopic effect) shows. Today, in the era of digital photograph, there are many software applications to produce anaglyph from a standard 2D digital image. Another method for viewing is 3D glasses fitted with variously polarized filters (with orthogonal or circular polarization). Also in this case, the resulting image consists of concurrent superposition of two component images taken by shifted cameras. The superposition is created on the projection screen by projection from two projectors fitted with polarization filters with different orientations or polarization directions. Viewer watches the screen with glasses with corresponding polarization filters of different polarization for each eye. Advantage of this somewhat more expensive method is reduced colour distortion of the colour perception. However, the projection screen is very expensive (specially treated silver canvas) because it may not change to polarization of incident and reflected light flux (depolarization).
Fundamental disadvantage of the solutions described above is the problem of time discontinuity of signals received by brain from eyes. The reason for this time discontinuity is the fact that signals going through left and right eye reach the brain vision centre with a time shift. This results in brain instability due to unnatural receipt of image signal. The vision centre must process the discontinued signal and the centre is not made for it. The consequences of this processing of received information may include epileptic fits or headaches. An alternative is successive stereoscopic imaging of the component images with eclipsing (Eclipse Method). The component images taken by shifted cameras are displayed on a display or projected to a projection screen successively. Their sequence may be equal to e.g. a period of half-frames. To reduce distortion in case of sequences of images of quick content change, the alternating period can be reduced—e.g. using 100 Hz exposition. Luminophores of the display (particularly green) or the projection screen used must not show long afterglow for the same reason. Also special glasses are required in this case. Apertures of left and right eye are successively eclipsed and opened in a synchronized way with alternating of the component images. The required synchronizing signal is usually emitted in the IR radiation band and this may practically restrict the viewing space and number of viewers. Technical applicability can be provided e.g. by LCD SH Shutter Glasses). For this version, the viewing angle is wider. For the last described method, signal is emitted concurrently from the first and second projector and the only difference between the signals is that one image has blue component blocked and the other has red component blocked. Because human eye is the most sensitive to green colour (up to 70% of image information consists of green colour), brain gets confused and human perceives the image as stereo image albeit slightly shifted in colour tones. Of course, this presents a different perception load but the problems described above (headache and epileptic fits) are mitigated. The last of the described methods could be implemented in passive asynchronous form where viewer's glasses function control is not required. In this case, the component images are projected in a time sequence by two projectors equipped with polarization filters with different polarization directions. The viewers use the glasses with corresponding polarization filters of different polarization for each eye similarly to the method described earlier. Disadvantage common for all 3D systems described in this section is the necessary use of special glasses. In addition, bibliography describes “Mesh-Based Depth Coding For 3d Video Using Hierarchical Decomposition Of Depth Maps”, Sung-Yeol Kim and Yo-Sung Ho, Gwangju Institute of Science and Technology (GIST) 1 Oryong-dong Buk-gu, 500-712, Gwangju, Korea). This article describes the process for 3D imaging based on a structure of triangle fields connected into the structure of a planar grid. The system is based on taking with right and left camera. Then, the photos taken from left and right camera superpose and where the image areas can be mutually defined and calculated, a triangle of single colour is defined with at least several points in each direction. Considering the side shift of right and left image it could be calculated which of the triangles would be higher and lower. The triangles being virtual and placed in a virtual centre produce a compact area that breaks depending on the space squeezing system. In this way, partial image plasticity could therefore be created. Whereas this triangle grid may behave, for example as metal sheet surface in a press mould, certain image profiling could be achieved, however, it is in no way possible to achieve neither high image depth dynamics as required for real imaging nor precise point structure. The problem is that surface is calculated by the areas of triangles and their squeezing up or down produces the illusion of space. However, this is still the compact grid with differently deformed triangle fields being unable to produce visual image fidelity. This system can work only as a demonstration of possibilities of the triangle fields when profiling of 2D image. However, it is important that when viewing the deformed 2D space, human beings cannot see a 3D image but partially profiled imprint of image surface only, created by colour areas and therefore without possibility of any definition of image details. No image definition in full depth dynamics occurs here but only a few per-cents when compared to real three-dimensional perception. In addition, the profiled image is created by triangle fields as non-existing central image with triangle structure of squeezed colour areas. This is a demonstration of possibilities of using the technology that is commonly only used in computer games. However, this technology is built for creation of virtual reality. Based on this procedure and calculation of the triangle grid it is almost impossible to get 3-D imagining being able to convince a human eye that it watches a real image.